1. Field of the Invention
The present invention relates to monomers of high temperature polyamides. Particularly, the present invention relates to cyclic terephthaldiamides that polymerize to form poly(terephthalamides).
2. Description of the Prior Art
The chemistry of polymerization of cyclic monomers or oligomers is well known in the polymer art. Such cyclic monomer polymerization processes have been utilized in polyamide applications, particularly for reaction injection molding (RIM) applications. Typically, in such a polymerization application, an anhydrous lactam (cyclic amide) is in-situ polymerized at or above 100.degree. C. in the presence of one or more of basic catalysts such as alkali and alkaline earth metals, their hydrides, hydroxides, alkoxides, oxides, alkyls or amides. Various lactams having 6-12 carbon atoms, such as caprolactam, pyrrolidone, piperidone, valerolactam and lauryllactam, have been known to be useful for in-situ polymerization processes. The advantage of the in-situ polymerization processes of lactam monomers, such as RIM, is based on the fact that the monomers employed are low melting and the polymers resulting therefrom are high melting and highly crystalline, and the polymerization process does not produce any byproducts. In addition, lactam monomers have low melt viscosity, obviating the need to utilize high pressure equipments necessary in conventional melt-injection molding processes.
Although the polyamides resulting from the above-mentioned process exhibit a range of valuable properties, they have disadvantages in that they are dimensionally unstable, because of their inherent hygroscopic property, and have limited high-temperature capabilities. Therefore, it is desirable to provide monomers or oligomers of polyamides that can be in-situ polymerized and have improved dimensional stability and high-temperature capability.
The polyamides derived from terephthalic acid and alkanediamines, which are commonly referred in the art as poly(terephthalamides), have been known in the art to exhibit high melting point and low moisture sensitivity. However, the high melting point of poly(terephthalamides), which is higher than 300.degree. C. and practically coincides with the thermal decomposition temperature of the polyamides, renders the production of the polymers by the conventional melt polymerization process unpracticable. Various publications have disclosed various methods of overcoming this polymerization difficulty. For example, U.S. Pat. No. 2,752,328 to Magat; U.S. Pat. No. 3,382,216 to Blaschke et al.; and U.S. Pat. No. 3,696,074 to Tsuda et al. disclose terephthalamide copolymer compositions having a lower crystalline morphology than homopolymer terephthalamides. Although such terephthalamide copolymers are melt. processible, they do not retain the benefits of crystalline polymers such as solvent resistance and various high temperature utilities including high heat deflection temperature. Therefore, it is desirable to produce poly(terephthalamides) of high crystallinity that have high temperature capabilities, dimensional stabilities and low moisture sensitivity, and to provide monomers of such poly(terephthalamides) that can be polymerized without utilizing the conventional polymerization processes which may thermally decompose the resulting poly(terephthalamides).
Stetter et al. disclosed in their article, "On Understanding Macrocyclic Ring System", Chem. Berichte, 91, 1775-1781 (1958), a range of macrocyclic diamides from aromatic dicarboxylic acids including 2,5-diaza-1,6-dioxo-[6](1,2)-orthocyclophane; 2,7-diaza-1,8-dioxo-[8](1,2)-orthocyclophane; 2,9-diaza-1,10-dioxo-[10](1,2)-orthocyclophane; 2,7-diaza-1,8-dioxo-[8](1,3)-metacyclophane; 2,9-diaza 1,10-dioxo-[10](1,3)-metacyclophane; 2,9-diaza-1,10-dioxo-[10](1,4)-paracyclophane; 2,11-diaza-1,12-dioxo-[12](1,4)-paracyclophane; 2,13-diaza-1,14-dioxo-[14](1,4)-paracyclophane; 1,1'-diaza-2,2'-dioxo-[2,2](1,2)-orthocyclophane; and 3,3'-diaza-4,4'-dioxo-[6,6](1,4)-paracyclophane. Of these cyclophanes, 2,11-diaza-1,12-dioxo-[12](1,4)-paracyclophane and 2,13-diaza-1,14-dioxo-[14](1,4)-paracyclophane exhibit molecular configurations that may polymerize. However, Stetter et al. did not recognize any use for the macrocyclic diamides they had synthesized.